The present invention relates to a process for preparation of alkylenebismelamines.
Alkylenebismelamines are useful compounds which can be used as components for forming resin materials, particularly aminoplasts, and flame retardants. As reported in J. Am. Chem. Soc., Vol. 73, pages 2984-2986 (1951), the prior process for preparation of alkylenebismelamines has been carried out by reacting 2-chloro-4,6-diamino-1,3,5-triazine with an alkylenediamine. Although the prior process is excellent in obtaining several substituted melamines, the process has a problem that raw materials therefor are not inexpensive.
In addition, it is known to replace an amino group of melamine by several amines such as alkylamine, arylamine or the like in the presence of an acidic catalyst [the method mentioned above is described in the following documents: DE 3422218 A1 (1985) (corresponding patents: EP 0166297 A1 (1986), JP 61010567 A (1986), U.S. Pat. No. 4,668,785 A (1987)), DE 3611420 A1 (1987) (corresponding patent: EP 0240867 A1 (1987)) and so on].
DE 3611420 A1 (1987) discloses that 10 mol or more of alkylenediamines are made to react with 1 mol of melamine to produce tris(aminoalkyl)melamine as substituted melamine, and dimer of the substitutedmelamines. Further, the document discloses that when 1 to less than 10 mol of alkylenediamines are made to react with 1 mol of melamine, the amount of the resulting tris(aminoalkyl)melamine decreases compared with the case wherein 10 mol or more of alkylenediamines are used, and that the amount of the oligomer and polymer of the substituted melamines increases.
However, the document does not disclose that alkylenebismelamines produced by the process of the present invention can be obtained in single-step.
The present inventors have studied eagerly in order to solve the problems describe d above, and found the process of the present invention in which alkylenebismelamines can be produced in single-step by reaction between alkylenediamines and melamines in the presence of an acidic catalyst.
It is an object of the invention to provide a process which enables easy and inexpensive preparation of alkylenebismelamines usable as components for forming resin materials, particularly aminoplasts, and flame retardants.
The invention relates to a process for preparation of an alkylenebismelamine of formula (2) 
(wherein R is a linear or branched C2-10 alkylene) by reacting an alkylenediamine of formula (1)
H2Nxe2x80x94Rxe2x80x94NH2xe2x80x83xe2x80x83(1)
(wherein R is a linear or branched C2-10 alkylene) with melamine in the presence of an acidic catalyst under heating, characterized in that the amount of melamine is at least twice that of the alkylenediarnine by mole.
R as a linear or branched C2-10 alkyene is, for example, ethylene, 1,2- or 1,3-propylene, tetramethylene, pentamethylene, 2,2-dimethyltrimethylene, hexamethylene, heptamethylene, octarnethylene or decamethylene.
The reaction of the present process may be usually carried, out by adding at least 2 moles of melamine to 1 mole of alkylenediamine in the presence of an acidic catalyst under heating. About 2 to 10 moles, preferably about 2 to 5 moles of melamine is added to 1 mole of alkylenediamine.
Solvents used, in the present process may be any solvents as long as the solvents dissolve at least a little melamines and diamines, have the boiling point not less than 120xc2x0 C., and do not participate in the reaction. The solvents are preferably alcohols such as ethylene glycol, diethylene glycol or the like.
Acidic catalysts used in the present process may be hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid, methanesulfonic acid or the like. These acids may be added in the free form or in the form of melamine salt, amine salt or ammonium salt, etc. The amount of acidic catalyst to be added is 1 to 100 mole %, preferably 2 to 30 mole % based on melamine.
The reaction is usually carried out under heated conditions, for example at temperatures of 120 to 500xc2x0 C., preferably at temperatures of 120 to 250xc2x0 C. The reaction may be effected at atmospheric pressure, or effected in an autoclave. It is preferable to distill away ammonia gas generated in the course of the reaction by passing nitrogen gas into the reaction solution thereby to achieve a reduction in the reaction time and an improving in the yield. The reaction time can be determined by confirming the consumption of raw materials and the formation of aimed compounds. Generally, the reaction time may be 1 to 24 hours.
The post-treatment of the reaction and the collection of aimed compounds may be carried out in the usual way. Usually, crystals are crystallized by adding water to the reaction solution after optionally concentrating the solvent thereof, and then purification such as recrystallization may be attained as the occasion demands to collect aimed compounds. A mixture of aimed compounds and melamine can be adequately used for a certain purpose. The method of purification and the purity of aimed compound may be determined if necessary.